Rubber hoses are usually composed of an inner tube, a reinforcing layer, and an outer cover with the inner tube and outer cover composed of a vulcanized rubber. Such a rubber hose requires a vulcanization step, and therefore, there is the problem that the manufacturing process becomes complicated. On the other hand, there is known a so-called thermoplastic resin tube which is simpler in the manufacturing process thereof in the point that the inner tube and outer cover are composed of a thermoplastic resin and no vulcanization step is required. However, the thermoplastic resin comprising this resin hose is generally harder compared with vulcanized rubber, and therefore, it is difficult to obtain a flexible hose. In addition, the thermoplastic resin will soften by heating and therefore, it is usually difficult at a temperature of 120.degree. C. or more.
Therefore, attempts have been made in the past to improve the flexibility by adding, to the thermoplastic resin, amorphous polymers such as a rubber (for example, see Japanese Unexamined Patent Publication (Kokai) No. 5-25374, Japanese Unexamined Patent Publication (Kokai) No. 6-64102, and Japanese Unexamined Patent Publication (Kokai) No. 6-207086), but there is the problem that the compatibility of the thermoplastic resin with rubber is poor and, if the blending amount of the rubber is increased to improve the flexibility in an acrylic rubber (ACM)/thermoplastic copolyester elastomer thermoplastic elastomer material, where the ACM composition is EA (ethyl acrylate)=40, BA (butyl acrylate)=32, MEA (methoxyethyl acrylate)=19, GMA (glycidyl methacrylate)=9 (wt %), the elongation will fall and, as a result, the breaking energy will be reduced and, in turn, the problem will arise of the hose performance falling.
Further, to improve the flexibility of a thermoplastic resin, there is known a resin hose comprised of a polyester thermoplastic elastomer having an inner tube of polybutylene terephthalate as a hard segment and polytetramethylene glycol or polycaprolactone as a soft segment, but this polyester thermoplastic elastomer is limited in the extent to which the hardness can be reduced to obtain the necessary heat softening resistance and strength properties. It is not possible to obtain a hose having a sufficient flexibility and heat resistance like that of a vulcanized rubber.
Therefore, development of a hose having sufficient flexibility which can be produced by a simple process not requiring a vulcanization step and a hose provided with heat resistance as well enabling use for transmission of pressure or transport of liquids at a high temperature has been desired. In response to this, there has been proposed a hose having an inner tube and an outer cover comprising a thermoplastic elastomer composed of a thermoplastic resin in which a vulcanized rubber (see Japanese Unexamined Patent Publication (Kokai) No. 6-64102) is dispersed.
This hose has an inner tube composed of a thermoplastic elastomer composition comprising a thermoplastic copolyester elastomer in which a vulcanized composition of at least one acrylic rubber having an acryl group and epoxy group is dispersed and has an outer cover composed of a thermoplastic elastomer composed of a thermoplastic resin in which a vulcanized rubber is dispersed. Further, the reinforcing layer is composed of a rayon fiber, polyester fiber, or hard steel wire or other organic fiber or inorganic wire such as stainless steel wire bonded with the inner tube and outer cover via an ordinary temperature-curing type urethane adhesive, etc.
By this configuration, it is possible to obtain a hose which is flexible at ordinary temperature and does not require a vulcanization step, but this hose is not necessarily satisfactory in terms of the low temperature properties, in particular, the flexibility at low temperature and cold resistance. Furthermore, the improvement in the oil resistance has been required.
Further, the high pressure resin hoses for use in construction machinery etc. should preferably be improved in abrasion resistance, heat softening resistance, flexibility, etc. In particular, there has been a strong need for the improvement in the abrasion resistance, resistance to heat softening resistance, flexibility, weather resistance, etc. of the outer cover of the hose. Furthermore, regarding the abrasion resistance, there is vibration and rocking in the environments where hoses are used, and therefore, the surface of the outer cover of the hose often rubs against adjacent metal members etc. and is abraded. In the past, an ether based polyurethane or other thermoplastic resin having abrasion resistance was used for the outer cover of such a hose, but this was insufficient for long term use. Therefore, studies have been made how to improve the problem by the polymer structure, but there have been the defects of impairment of the flexibility. In this way, up until now, there has not been a thermoplastic elastomer composition which is superior in abrasion resistance, heat softening resistance, flexibility, etc. and can be suitably used for the outer cover of a hose.
In the past, in the bonding of an olefin thermoplastic elastomer composition and polyester fiber, no technique for stably bonding them, in particular, no olefin thermoplastic elastomer composition having a high temperature resistant bondability capable of withstanding, stress due to repeated deformation at a high temperature such as 120.degree. C. was known. This was because an olefin thermoplastic elastomer composition is a nonpolar substance and has a low surface energy, while a polyester fiber has polarity. Therefore, in general the bondability between the composition and the fiber is poor. In particular, it is not possible to maintain the strength of the bond at a high temperature.
To solve this problem, for example, a formulation using a so-called primer and adhesive system/adhesive resin has been proposed, but there is still not known an adhesive formulation or an olefin thermoplastic elastomer composition giving a bond of a strength capable of withstanding the repeated deformation at a high temperature such as 120.degree. C. In particular, in a hose, a dynamically vulcanized olefin thermoplastic elastomer composition has suitable properties as the outer cover material comprising the hose and a polyester fiber has suitable properties as a reinforcing fiber layer material comprising the hose, but there is not yet known an adhesive formulation for bonding the composition and the fiber, in particular, an adhesive formulation of a strength capable of withstanding the stress of repeated deformation at the environment of use of high pressure flexible hoses, that is, a high temperature such as 120.degree. C. No hose combining these materials is therefore known.
Accordingly, there has been a desire for an olefin thermoplastic elastomer composition having bondability with a polyester fiber and capable of withstanding the stress of repeated deformation at a high temperature such as 120.degree. C. and a laminate using the above thermoplastic elastomer composition and a polyester fiber.
There is known a hose comprising an inner tube, reinforcing layer, and outer cover laminated in that order. In this hose, the inner tube and outer cover are composed of a vulcanized rubber or urethane, polyester, or nylon, or other plastics and the reinforcing layer is composed of nylon, polyester, rayon, vinylon, or aromatic polyamide fiber or other fiber braided or wrapped in a spiral. Between these layers, bonding is performed using a rubber cement or urethane adhesive etc.
However, the so-called "rubber hose" using rubber in the outer cover requires a vulcanization step, and therefore, the manufacturing process becomes complicated. Further, a so-called resin hose using just a thermoplastic resin for the inner tube and outer cover is hard and poor in flexibility and, when bent, has the problem of formation of kinks. As one proposal for solving this problem, there has been proposed a hose using a thermoplastic elastomer composition comprising a polyolefin based thermoplastic resin, polyvinyl chloride based thermoplastic resin, polyamide based thermoplastic resin, polyester based thermoplastic resin, or other thermoplastic resin in which an at least partially cross-linked vulcanized rubber phase, is dispersed (for example, see Japanese Unexamined Patent Publication (Kokai) No. 6-64102).
Among these thermoplastic elastomer compositions, a thermoplastic elastomer composition composed of a polyolefin thermoplastic resin and an at least partially cross-linked elastomer component blended therein, is high in flexibility and suitable as a material for the inner tube and outer cover of the hose. However, there has not yet been developed an adhesive exhibiting excellent bondability to both a fiber reinforcing layer composed of a polyester, nylon, rayon, or other fiber and a thermoplastic elastomer composition composed of a polyolefin thermoplastic resin and an at least partially cross-linked elastomer component blended therein.
For example, as methods for improving the adhesiveness of the main component of the thermoplastic elastomer composition, that is, the polyolefin thermoplastic resin, there are known corona discharge, UV irradiation, flame treatment, strong acid treatment, and other surface activation methods. With these methods, however, not only is it difficult to secure the level of bonding required for hoses and other durable products composed of a thermoplastic elastomer composition, but also the process of application to a manufacturing line of a hose is extremely complicated and very high in cost, and therefore, is not practical.
Further, elastomer compositions are used as various sealing agents, rubber hoses, and other industrial products and also for other rubber products. In particular, epoxy group-containing acrylate copolymer rubbers containing (meth)acrylic acid esters etc. are elastomer compositions known to be superior in oil resistance and aging resistance and, when cross-linked, cold resistance or strength properties as well. There is the problem, however, that a sufficient elongation and compression set resistance cannot be obtained with a conventional cross-linking agent (polyfunctional carboxylic acid).
On the other hand, in recent years, thermoplastic elastomer compositions provided with both the advantages of a rubber and thermoplastic resin have been developed using the dynamic vulcanization (dynamic cross-linking) of rubber, but when selecting an acrylate copolymer as the rubber component, in particular when using an epoxy group as the cross-linking site of the acrylate copolymer so as to obtain an elastomer composition not including an amine component, since an amine component would promote the deterioration of the polyester, there is the problem that a sufficient elongation and compression set resistance cannot be obtained. For example Japanese Unexamined Patent Publication (Kokai) No. 1-92251 discloses a rubber composition composed of an ethylene copolymer rubber and acrylic rubber offering a balance of cold resistance, oil resistance, resistance to aging by heat, and strength properties. Further, Japanese Unexamined Patent Publication (Kokai) No. 5-25347 discloses a high stress resistant thermoplastic elastomer composition composed of a thermoplastic copolyester or copolyamide elastomer and epoxy-containing (meth)acrylate copolymer rubber which is flexible and gives a superior heat resistance and compression set resistance.
Further, Y. Tsukahara et al, International Rubber Conference Full Texts, p. 74 (1995) and Japanese Unexamined Patent Publication (Kokai) No. 7-304902 disclose a natural rubber composition as an environmentally friendly elastomer material composed of epoxylated natural rubber and terminal carboxylated polycaprolactone which is excellent in fluidity and is superior in the elastic modulus of the rubber, elongation, and oil resistance.
As explained above, these various elastomer compositions and thermoplastic elastomer compositions have superior performance, but have the problem that a practically sufficient elongation and compression set resistance cannot be obtained.
The present inventors previously proposed a hose having at least an inner tube, reinforcing layer, and outer cover, where the inner tube is a thermoplastic elastomer composition having a structure of a matrix of a thermoplastic copolyester elastomer and vulcanized rubber particles of an acrylic rubber having an acryl group and epoxy group dispersed therein and containing 30 to 90% by weight of the thermoplastic copolyester elastomer component and 70 to 10% by weight of the vulcanized rubber component of the acrylic rubber, the reinforcing layer is composed of a polyester fiber etc., the outer cover is a thermoplastic elastomer having a structure of a matrix of a thermoplastic copolyester elastomer and vulcanized rubber particles of an acrylic rubber having an acryl group and epoxy group dispersed therein and containing 30 to 90% by weight of the thermoplastic copolyester elastomer component and 70 to 10% by weight of the vulcanized rubber of the acrylic rubber component, and an adhesive is disposed at least between the reinforcing layer and the outer cover (Japanese Patent Application No. 8-23903). That is, they proposed a hose wherein, by selection of the material of the inner tube and outer cover of the hose, it was possible to improve the hose flexibility at ordinary temperature and low temperature, oil resistance, and cold resistance and further reduce the production costs by making it possible to produce it, without requiring a vulcanization step.
In this hose, however, a urethane ordinary temperature-curing type adhesive etc. are used as the bonding layer. Since the adhesive was a reactive type, heat curing occurred due to the heat during use, and therefore, the bonding layer became hard and in turn the filaments of the fibers of the reinforcing layer broke causing the reinforcing layer to break and the durability to fall. Even if using a polyester type hot melt adhesive resin in place of this, the adhesive resin detracts from the thermoplasticity and is poor in heat softening resistance, and therefore, a hose which is satisfactory in durability (high temperature impact pressure test: 120.degree. C., 27.5 MPa) cannot be obtained.
In the past, hoses composed of an inner tube, reinforcing layer, and outer cover with an inner tube and outer cover made out of a thermoplastic resin composition, thermoplastic elastomer composition, or other thermoplastic material have been capable of reducing production costs since they do not require a vulcanization step. These hoses have, therefore, come into wide use. In these conventional hoses, the bonding between the inner tube and the reinforcing layer and the bonding between reinforcing layers have been performed using moisture curing type urethane adhesives and other ordinary temperature-curing type adhesives or using copolyester resin or olefin resin or other hot melt type adhesive resins and heating after the formation of the inner tube, reinforcing layer, and outer cover so as to melt the adhesive resin and cause bonding. Further, hoses which use a high rigidity thermoplastic resin for at least one of the inner tube and outer cover, whereby do not require bonding of the inner tube and reinforcing layer or bonding between the reinforcing layers are being used.
However, with a hose using an ordinary temperature-curing type adhesive, since the adhesive is a reactive type, it cures with heat during use. The bonding layer becomes hard and, when the hose is subjected to repeated bending or pressure changes, the hardening of the bonding layer causes the fibers of the reinforcing layer to break and causes a problem in the durability of the hose. Further, if a hot melt type adhesive resin is used, due to the limitations in the order of formation of the layers, with ordinary processes of production, there is no bond between the bonding layer and the layer above it, and therefore it is necessary to heat the bonding layer to cause it to bond with the layer above it. Since this means heating from the outside of the hose after the formation of the outer cover until the adhesive resin melts, an excessive amount of heat is given to the hose. This causes dimensional changes in the hose or uneven tension to the fibers of the reinforcing layer, whereby the uniformity of the hose is impaired and sufficient durability is made impossible. Further, in recent years, there have been strong demands for making hoses more flexible for the purpose of hose attachment, but a hose using a low rigidity (or flexible) thermoplastic material for the inner tube and not having the layers bonded to each other has problems in terms of its durability, and therefore, large problems in use. Further, in the case of an ordinary temperature-curing type adhesive, an organic solvent is used, and therefore, there are problems in terms of the environment. In the case of a hot melt type adhesive, there are problems in the productivity due to the heat treatment step after the formation of the outer cover.
In the past, further, a high pressure hose has, for example, been composed of an inner tube having a thermoplastic resin material for at least the outer circumference of the inner tube, at least one reinforcing layer composed of reinforcing yarn braided around the outer circumference of the inner tube, and an outer cover covering the surface of the same. In such a hose, however, the bondability between the inner tube having a thermoplastic resin material for at least the outer circumference of the inner tube and the reinforcing yarn braided around the outer circumference of the inner tube and the bondability between two or more reinforcing layers has a major influence on the flexibility and durability of the hose. If the bondability is poor, the inner tube and the reinforcing yarn will separate or the reinforcing layers will separate--adversely influencing the performance of the hose. In the past, the reinforcing yarn was braided around the outer circumference of the inner tube composed of the thermoplastic resin material or, further, when there were two or more reinforcing layers, a solvent based adhesive was used, the reinforcing yarn braided around the outer circumference of the inner tube, and the reinforcing layers bonded. There were also cases of use of means other than solvent type adhesives such as the use of infrared rays, far infrared rays, near infrared rays, ultrasonic waves, high frequency heating, electrical induction heating, etc. to heat an inner tube composed of a thermoplastic resin material or an adhesive resin layer composed of a thermoplastic resin material arranged between two or more reinforcing layers after the formation of the hose by an oven or other heating apparatus from the outer surface of the outer cover so as to bond the inner tube and the reinforcing yarn or the reinforcing layers. When a solvent type adhesive is used, however, there tend to be problems in safety and health or problems of pollution due to the evaporation of the solvent, one or two days are required for the aging for achieving a practical strength, and it was difficult to improve the productivity. Further, in the case of the latter method of using a heating apparatus, the component parts have been subjected to aggravated dimensional changes, aging, etc. and therefore, the effect on the quality has been high (heating of just the surface of the target object has been impossible), there have been limitations as to the installation space, the equipment has been high in price and large in size, and there have been other problems. Therefore, it is clear that there have been many problems in the method of bonding the above conventional inner tube and the reinforcing yarn or the bonding between reinforcing layers.